1. Technical Field
The inventions disclosed in this application relate to methods for winding an automotive tire building strip member on a building drum.
More particularly, the first invention in this application provides a method for winding a strip member, such as rubberized steel cord, tread rubber or the like, precut to the circumferential length of the building drum of a tire building machine, on the building drum in such a manner that both ends of the strip member will be exactly abutted against each other on the drum.
The second invention in this application relates to an automotive tire building device wherein the lapping margin of ends of a strip member wound on a building drum can be automatically measured.
2. Prior Art
In winding a tire strip member on a building drum, it is at times required to insure exact abutment of its ends and at other times required that the lapping margin (positive and negative) be within certain allowable limits.
As a technology for insuring exact abutment of both ends of a strip member, such as rubberized steel cord or tread rubber, in the winding thereof on the building drum of an automotive or other tire building machine, there is known a method described in Japanese Patent Publication No. 61-32980. According to this method, the length of the strip precut to the circumferential length of the building drum is measured and, then, a leading portion, of predetermined length, of the strip is taken up on the building drum at the feeding (takeup) speed equal to the peripheral speed of the drum. Then, the feeding speed relative to the building drum speed is altered to either compress or stretch the strip while its intermediate portion is wound on the building drum. Finally, the feeding speed is re-equalized with the peripheral speed of the building drum to wind up the remaining portion of the strip member on the drum.
However, the strip member tends to shrink with the progress of time after cutting and the time to termination of shrinkage and the amount of shrinkage is dependent on the environment and other conditions. Under certain conditions, the amount of post-cutting shrinkage reaches as much as about 0.5%. Mor over, the length of the strip member varies with the magnitude of the tension that acts on the strip when it is transferred from a transfer conveyer to the building drum and the pressure of contact between the strip and the drum. In the prior art method mentioned above the total length of the strip member is measured while it is undergoing shrinkage after cutting and the ratio of the feeding speed to the peripheral speed of the building drum is set according to the length value thus found so as to compress or stretch the intermediate portion of the strip. As a consequence, the aforesaid ratio is often irrelevant and there occurs an excess or a shortage of compression or stretching of the strip member, thus causing a lapping of the leading and trailing ends of the strip member or a gap therebetween.
Therefore, in the first invention in this application provides a winding method which insures exact abutment of the ends or abutment without an appreciable overlap or gap.
Furthermore, in the process of manufacture of an automotive tire, not only the steel cord and tread rubber mentioned above but a variety of other rubber-based strip members are cut to length and both ends thereof are joined to build single-layer or multi-layer ring or cylindrical members. For example, on the primary building machine, an inner liner (a strip member of rubber) and a plurality of ply cords (rubberized fiber cords or steel cords), all precut to the circumferential length of the building drum, are laid up on the peripheral surface of the drum. In the secondary building machine, two steel belts (rubberized steel cords), a cap ply (rubberized nylon cord), etc. are laid up some of these different strip members are not joined by abutment at ends as described above but are joined by lapping the trailing end over the leading end on the drum. As mentioned above, the strip member has the property to shrink on standing after cutting to length as mentioned above and the amount of this shrinkages varies with changes in environment. Also as mentioned above, the length of the strip member is altered by external forces that act on the strip when it is transferred from the conveyer to the drum. Therefore, even if the strip member has been cut precisely to length, a variation is inevitable in the degree of lapping of both ends. Therefore, it is common practice for the operator to trim off the rubber or cord at the trailing end when the degree of lapping is too large or unwind the strip partway and rewind it with stretching when there is a gap between ends.
However, the conventional tire building machine is not equipped with very effective means for inspecting the end joint of the strip member and the current trend toward automation of tire building cannot completely avoid a risk of products with the surplus or deficiency in end lapping being shipped uncorrected and marketed.
Accordingly the second invention in this application provides a tire building device which is capable of detecting a surplus or deficiency in end lapping while a strip member is wound on a building drum of the primary or second building machine.